Heat Exchange and Method of Manufacturing the Same

ABSTRACT

In a heat exchanger having a core portion in which aluminum flat tubes and aluminum fins are disposed alternatively and brazed with each other, each fin has one side portion located at one side of the tube and the other side portion located at the other side of the tube. The one side portion of the fin is higher in pitting potential than the other side portion of the fin, and the pitting potential difference between the one side portion of the fin and the other side portion of the fin is 40 to 200 mV. The pitting potential difference can be formed by the Zn concentration difference in the aluminum alloy constituting the fin.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is an application filed under 35 U.S.C. §111(a)claiming the benefit pursuant to 35 U.S.C. §119(e)(1) of the filing dateof U.S. Provisional Application No. 60/598,539 filed on Aug. 4, 2004,pursuant to 35 U.S.C. §111(b).

This application claims priority to Japanese Patent Application No.2004-221861 filed on Jul. 29, 2004 and U.S. Provisional Application No.60/598,539 filed on Aug. 4, 2004, the entire disclosures of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a heat exchanger to be manufactured bybrazing, and more particularly to a heat exchanger capable ofdemonstrating excellent fin strength even in the case of an occurrenceof fin corrosion. It also relates to a method of manufacturing the heatexchanger.

In this disclosure, the wording of “aluminum” is used to include themeaning of aluminum and its alloy. Furthermore, the wording of “Al,”“Mn,” and “Zn” denotes metal simple substance, respectively.

BACKGROUND ART

Conventionally, as a heat exchanger for use in a vehicle such as anautomobile, an aluminum laminate type heat exchanger having a coreportion with flat tubes and fins disposed alternatively has been widelyused. In such a heat exchanger, it is required to demonstrate heatexchanging performance even in the case of an occurrence of fincorrosion, and also required to have certain strength against chippings,etc. In general, after the occurrence of fin corrosion, the fin strengthdeteriorates due to intergranular corrosion.

In order to attain excellent material strength even in the case of anoccurrence of fin corrosion, it has been known to use an aluminum alloybrazing sheet as a heat exchanger fin improved in intergranularcorrosion resistance by regulating chemical composition of the corematerial and skin material. Also proposed is a method of preventingintergrannular corrosion of fins by regulating brazing conditions (seeJapanese Unexamined Laid-open Patent Publication Nos. H11-140572 and2003-326359).

However, the aforementioned methods of preventing intergranularcorrosion could not sufficiently improve the self-corrosion resistanceof fins, and therefore the fin strength could not be maintained under asevere condition exceeding a certain corrosion environment level.

In view of the aforementioned background technique, the presentinvention aims to provide a heat exchanger excellent in strength even inthe case of an occurrence of corrosion, especially a heat exchangerhaving an excellent fin strength of a heat exchanger core front siderequiring chipping proof performance. It also aims to provide a methodof manufacturing the heat exchanger.

DISCLOSURE OF INVENTION

To attain the aforementioned objects, the heat exchanger according tothe present invention has the following structure as recited in thefollowing Items [1] to [9].

[1] A heat exchanger having a core portion in which aluminum flat tubesand aluminum fins are disposed alternatively and brazed with each other,each fin having a one side portion located at one side of the tube andthe other side portion located at the other side of the tube,

wherein the one side portion of the fin is higher in pitting potentialthan the other side portion of the fin, and

wherein the pitting potential difference between the one side portion ofthe fin and the other side portion of the fin is 40 to 200 mV.

[2] The heat exchanger as recited in the aforementioned Item 1, whereinthe pitting potential difference is created by Zn concentrationdifference in aluminum alloy constituting the fin.

[3] The heat exchanger as recited in the aforementioned Item 2, whereinthe Zn concentration difference is 0.4 mass % or more.

[4] The heat exchanger as recited in the aforementioned Item 1, whereinthe one side portion of the fin and the other side portion of the finare constituted by separated fins consisting of one side fin located atone side of the tube and the other side fin located at the other side ofthe tube, the separated fins being disposed with a distance therebetweenalong the longitudinal direction of the tube.

[5] The heat exchanger as recited in the aforementioned Item 4, whereinthe distance between the one side fin and the other side fin is 3 mm orless.

[6] The heat exchanger as recited in the aforementioned Item 4 or 5,wherein the one side fin is made of aluminum alloy consistingessentially of Mn: 0.8 to 2 mass %, Zn: 0.4 to 2 mass %, and the balancebeing Al and inevitable impurities, and wherein the other side fin ismade of aluminum alloy consisting essentially of Mn: 0.8 to 2 mass %,Zn: 1.5 to 3 mass %, and the balance being Al and inevitable impurities.

[7] The heat exchanger as recited in the aforementioned Item 1, whereinthe one side portion of the fin and the other side portion of the finare made of an integrated single fin, wherein pitting potentialdifference is formed between the one side portion and the other sideportion.

[8] The heat exchanger as recited in the aforementioned Item 7, whereinthe one side portion of the fin is made of aluminum alloy consistingessentially of Mn: 0.8 to 2 mass %, Zn: 0.4 to 2 mass %, and the balancebeing Al and inevitable impurities, and wherein the other side portionof the fin is made of aluminum alloy consisting essentially of Mn: 0.8to 2 mass %, Zn: 1. 5 to 3 mass %, and the balance being Al andinevitable impurities.

[9] The heat exchanger as recited in the aforementioned Item 1, whereinthe fin has a thickness of 100 μm or less.

The heat exchanger for use in a vehicle according to the presentinvention has the following structure as recited in the following Item[10].

[10] A heat exchanger for use in a vehicle, the heat exchanger having acore portion in which aluminum tubes and aluminum fins are disposedalternatively and brazed with each other, each fin having one sideportion located at one side of the tube and the other side portionlocated at the other side of the tube,

wherein the one side portion of the fin is higher in pitting potentialthan the other side portion of the fin,

wherein the pitting potential difference between the one side portion ofthe fin and the other side portion of the fin is 40 to 200 mV, and

wherein the heat exchanger is installed on a vehicle with the one sideportion of the fin with higher pitting potential facing toward a frontside of the vehicle and the other side portion of the fin with lowerpitting potential facing toward a rear side of the vehicle.

Furthermore, the method of manufacturing a heat exchanger according tothe present invention has the following structure as recited in thefollowing Items [11] to [13].

[11] A method of manufacturing a heat exchanger having a core portion inwhich aluminum flat tubes and aluminum fins are disposed alternativelyand brazed with each other, each fin having one side portion located atone side of the tube and the other side portion located at the otherside of the tube, the one side portion of the fin being higher inpitting potential than the other side portion of the fin,

the method, comprising the steps of:

provisionally assembling a core portion by alternatively disposing thetubes and the fins; and

heating the provisionally assembled core portion in a furnace to brazethe tubes and the fins.

[12] A method of manufacturing a heat exchanger having a core portion inwhich aluminum flat tubes and aluminum fins are disposed alternativelyand brazed with each other, each fin having one side portion located atone side of the tube and the other side portion located at the otherside of the tube, the one side portion of the fin being higher inpitting potential than the other side portion of the fin,

the method, comprising the steps of:

provisionally assembling a core portion by alternatively disposing thetubes and the fins; and

heating the provisionally assembled core portion in a furnace in a statein which an Al—Zn alloy plate is disposed neat the other side portion ofthe fin to braze the tubes and the fins.

[13] A method of manufacturing a heat exchanger having a core portion inwhich aluminum flat tubes and aluminum fins are disposed alternativelyand brazed with each other, each fin having one side portion located atone side of the tube and the other side portion located at the otherside of the tube, the one side portion of the fin being higher inpitting potential than the other side portion of the fin,

the method, comprising the steps of:

provisionally assembling a core portion by alternatively disposing thetubes and the fins;

applying flux only to the other side portion of the fin of theprovisionally assembled core portion; and

heating the provisionally assembled core portion to which the flux isapplied to the other side portion of the fin in a furnace to braze thetubes and the fins.

EFFECTS OF THE INVENTION

According to the heat exchanger as recited in the aforementioned Item[1], since cathodic protection is given to the one side portion of thefin, the strength deterioration at the one side portion of the fin canbe restrained, and therefore certain fin strength can be maintained atthe one side portion even after an occurrence of corrosion.

According to the heat exchanger as recited in the aforementioned Item[2], the Zn concentration difference causes pitting potentialdifference, which restrains strength deterioration at the one sideportion of the fin. Furthermore, the Zn contained in the fin can givecorrosion protection to the tube.

According to the heat exchanger as recited in the aforementioned Item[3], sufficient corrosion protection can be given to the one sideportion of the fin.

According to the heat exchanger as recited in the aforementioned Item[4], since two separated fins are used, it is possible to adjust thepitting potential difference in the fin even before the brazing byadjusting the composition of the fin material.

According to the heat exchanger as recited in the aforementioned Item[5], sufficient cathodic protection effect can be obtained in the heatexchanger using two separated fins disposed between adjacent tubes.

According to the heat exchanger as recited in the aforementioned Item[6], sufficient cathodic protection effect can be obtained in the heatexchanger using two separated fins disposed between adjacent tubes, andthe heat exchanger can be excellent in buckling resistance at hightemperature due to the Mn contained in the fin.

According to the heat exchanger as recited in the aforementioned Item[7], sufficient cathodic protection effect can be obtained in the heatexchanger using an integrated single fin disposed between adjacenttubes.

According to the heat exchanger as recited in the aforementioned Item[8], sufficient cathodic protection effect can be obtained in the heatexchanger using an integrated single fin disposed between adjacenttubes, and the heat exchanger can be excellent in buckling resistance athigh temperature due to the Mn contained in the fin.

According to the heat exchanger as recited in the aforementioned Item[9], the heat exchanger can be excellent in fin strength, lightness, andheat releasing performance.

According to the heat exchanger as recited in the aforementioned Item[10], since certain strength can be maintained at the front side of thefin even in the case of an occurrence of corrosion, damages due tochippings can be decreased.

According to the method of manufacturing the heat exchanger as recitedin the aforementioned Item [11], it is possible to manufacture a heatexchanger having pitting potential difference between one side portionand the other side portion of the fin by the material compositionadjustment of the two separate fins.

According to the method of manufacturing the heat exchanger as recitedin the aforementioned Item [12], the Zn which will evaporate from theAl—Zn alloy plate at the time of heating will diffuse into the fin, andan inclination of Zn concentration depending on the distance from theAl—Zn alloy plate will be generated. As a result, the Zn concentrationof the other side portion of the fin near the Al—Zn alloy plate becomeshigher and that of the one side portion thereof becomes lower.Therefore, a heat exchanger having a pitting potential difference basedon the Zn concentration difference can be provided.

According to the method of manufacturing the heat exchanger as recitedin the aforementioned Item [13], since Zn evaporation at the other sideportion of the fin to which flux is applied is restrained during theheating step, the Zn concentration becomes relatively higher than theone side portion of the fin. Thus, a heat exchanger having a pittingpotential difference based on the Zn concentration difference can beprovided.

BRIEF DESCRIPTION OF DRAWINGS

The preferred embodiments of the present invention are shown by way ofexample, and not limitation, in the accompanying figures, in which:

FIG. 1 is a front view of a heat exchanger according to an embodiment ofthis invention;

FIG. 2 is a perspective view partially showing a core portionconstituting the heat exchanger in which a single fin is disposedbetween adjacent tubes; and

FIG. 3 is a perspective view partially showing a core portionconstituting the heat exchanger in which two separated fins arranged inparallel are disposed between adjacent tubes.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a front view of a heat exchanger according to an embodiment ofthis invention. This heat exchanger 1 is the so-called multi-flow typeheat exchanger used as a condenser for use in a refrigeration cycle inan automobile air conditioner. FIGS. 2 and 3 show an enlarged principalportion of the heat exchanger shown in FIG. 1 in a brazing positionrotated by 90 degrees for an explanation purpose.

In detail, in this heat exchanger 1, between a pair of right and leftvertical hollow headers 2 and 2 disposed in parallel with each other, aplurality of heat exchanging tubes 10 are disposed in parallel withtheir opposite sides fluidly communicated with the hollow headers 2 and2. A corrugate fin 20 is disposed between adjacent heat exchanging tubes10 and outside the outermost corrugate fin 20. Outside the outermostcorrugate fin 20, a side plate 4 is disposed.

The heat exchanging tube 10 is an aluminum hollow extruded article. Asshown in FIG. 2, the inner side thereof is divided by partition walls 11extending in the longitudinal direction into a plurality of refrigerantpassages 12.

The heat exchanger 1 is manufactured as follows. The aforementioned heatexchanging tubes 10 and fines 20 are stacked alternatively and theopposite ends of the heat exchanging tubes are inserted in thecorresponding insertion slots formed in the headers 2 to form aprovisionally assembled core portion 3. Furthermore, side plates 4 and 4are provisionally assembled to the core portion 3. Then, thisprovisional assembly is integrally brazed in a furnace.

In the fin 20, the widthwise one side portion 20 a thereof is set to behigher in pitting potential than the other side portion 20 b thereof sothat the other side portion 20 a can be preferentially corroded tothereby give cathodic protection to the one side portion 20 a of the fin20. Due to this cathodic protection, the one side portion 20 a of thefin 20 can be maintained in strength even if the fin 20 is corroded tosome extent.

The pitting potential difference should fall within the range of from 40to 200 mV. If the pitting potential difference is less than 40 mV, thecathodic protection cannot be attained, which makes it difficult to givecorrosion protection to the one side portion 20 a of the fin 20. On theother hand, if the pitting potential difference exceeds 200 mV, quickcorrosion occurs to cause corrosion of the one side portion 20 a,resulting in deteriorated fin strength. The preferable pitting potentialdifference is 50 to 150 mV.

The aforementioned pitting potential difference can be preferablyattained by changing the Zn concentration in an aluminum alloyconstituting the fin 20, i.e., setting the Zn concentration at the otherside portion 20 b of the fin 20 to be relatively higher than the oneside portion 20 a thereof. In this case, it is preferable that the Znconcentration difference is 0.4 mass % or more because of the followingreasons. If it is less than 0.4 mass %, only small pitting potentialdifference can be obtained, resulting in insufficient cathodicprotection. The preferable Zn concentration difference is 0.6 mass % ormore. Although the present invention does not limit the upper limit ofthe Zn concentration difference, the preferable Zn concentrationdifference is 2.5 mass % or less to avoid excessive corrosion of theother side portion 20 b of the fin 20.

The following compositions can be recommended as fin compositions withthe aforementioned pitting potential difference.

The one side portion 20 a of the fin 20 is preferably made of analuminum alloy consisting essentially of Mn: 0.8 to 2 mass %, Zn: 0.4 to2 mass %, and the balance being Al and inevitable impurities. On theother hand, the other side portion 20 b of the fin 20 is preferably madeof an aluminum alloy consisting essentially of Mn: 0.8 to 2 mass %, Zn:1.5 to 3 mass %, and the balance being Al and inevitable impurities.

In the aforementioned alloy compositions, Mn is an essential element forenhancing fin strength and attaining buckling resistance at hightemperature. If the Mn concentration is less than 0.8 mass %, theaforementioned effect is poor. However, if it exceeds 2 mass %, roughintermetallic compounds will be generated, resulting in deterioratedworkability. The prefereable Mn concentration is 0.9 to 1.7 mass %.

For the purpose of giving cathodic protection to the tube 10 by the fin20, it is preferable that the one side portion 20 a of the fin 20 alsocontains a small amount of Zn. The preferable Zn concentration in theone side portion 20 a of the fin 20 is 0.4 to 2 mass % because of thefollowing reasons. If it is less than 0.4 mass %, the cathodicprotection effect is poor. However, if it exceeds 2 mass %, the pittingpotential difference between the one side portion 20 a and the otherside portion 20 b becomes smaller, resulting in poor cathodic protectioneffect at the one side portion 20 a. More preferably, the Znconcentration in the one side portion 20 a of the fin 20 falls withinthe rang of from 0.8 to 1.8 mass %. On the other hand, the preferable Znconcentration of the other side portion 20 b of the fin 20 is 1.5 to 3mass % because of the following reasons. If it is less than 1.5 mass %,the concentration difference between the one side portion 20 a of thefin 20 and the other side portion 20 b thereof is small, which makes itdifficult to secure a prescribed pitting potential difference. On theother hand, if it exceeds 3 mass %, quick corrosion occurs to therebycause corrosion of the one side portion 20 a, resulting in deterioratedfin strength. More preferably, the Zn concentration in the other sideportion 20 b of the fin 20 falls within the range of from 1.8 to 2.7mass %.

In the example shown in FIG. 2, one fin is disposed between adjacenttubes 10 and 10. This fin 20 is differentiated in Zn concentrationbetween the one side portion 20 a of the fin 20 and the other sideportion 20 b thereof, and therefore there is pitting potentialdifference therebetween. In this invention, as shown in FIG. 3, twoseparated fins different in pitting potential due to differentiated Znconcentration, one side fin 21 a with higher pitting potential and theother side fin 21 b with lower pitting potential, can be disposed inparallel between the adjacent tubes 10 along the longitudinal directionof the tube 10. In this alternative example, the preferable compositionsof the aluminum alloy constituting the one side fin 21 a and the otherside fin 20 b can be the same as those constituting the one side portion20 a of the fin 20 and the other side portion 20 b of the fin 20 shownin FIG. 2.

In the case of employing the aforementioned two fins 21 a and 21 b to bedisposed between adjacent tubes 10 and 10, it is preferable that thedistance D between the adjacent fins is 3 mm or less, more preferably 2mm or less.

The thickness of the fin 20, 21 a and 21 b is preferably set to 100 μmor less so as to secure fin strength even after an occurrence ofcorrosion and obtain lightness, heat releasing performance andworkability. More preferably, the thickness of the fin falls within therange of from 50 to 90 μm.

In this invention, there are two types of fins. In one type, a fin isconstituted by two portions clearly different in pitting potential, oneportion with higher pitting potential and the other portion with lowerpitting potential. In the other type, pitting potential graduallychanges from one side portion to the other side portion of a fin.Accordingly, there are two types from the view point of Znconcentration. That is, in one type, a fin is constituted by twoportions clearly different in Zn concentration, one portion with high Znconcentration and the other portion with low Zn concentration. In theother type, the Zn concentration gradually changes from one side portionto the other side portion. It should be noted that both types fallwithin the scope of the present invention.

In the heat exchanger according to the present invention, even ifcorrosion occurs to some extent, the one side portion can be maintainedin fin strength than the other side portion over a long period.Therefore, this heat exchanger is suitable for a heat exchanger to bedisposed at a location where strength and durability are required at oneside of the core portion. For example, in a heat exchanger mounted in avehicle such as an automobile, since chippings occur at the front sideof the core portion, it is required that the front side of the fin ishigher in strength than the rear side thereof. Accordingly, it ispossible to cope with chippings and fin damages by installing the heatexchanger according to the present invention with one side of the coreportion, i.e., one side portion of the fin with high pitting potential,facing frontward and the other side facing rearward.

In manufacturing the heat exchanger according to the present invention,there are various methods for differentiating Zn concentration betweenone side portion of the fin and the other side portion of the fin. Thepresent invention allows any one of methods for differentiating Znconcentration, and does not limit to any one of them.

The Zn concentration in the aluminum alloy constituting the fin afterbrazing is decided by the sum of the Zn amount contained in the fincomposition before brazing, the Zn amount supplied from outside duringthe brazing and the decreased amount of Zn evaporated by the heat duringthe brazing.

The alloy composition of the fin before brazing can be arbitrarilyadjusted at the time of casting the material. Accordingly, inmanufacturing the heat exchanger using two pieces of fins 21 a and 21 bas shown in FIG. 3, two types of fins, one side fin 21 a with lower Znconcentration and the other side fin 21 b with higher Zn concentration,are manufactured, and then disposed between adjacent tubes 10 and 10along the longitudinal direction of the tube to obtain a provisionallyassembled core portion 3. Then, this provisionally assembled coreportion 3 is brazed in accordance with any known method. As a result, aheat exchanger having a fin different in Zn concentration between theone side portion and the other side portion can be manufactured.

As a method of supplying Zn from outside at the time of brazing, amethod shown in FIG. 2 can be exemplified. In this method, tubes 10 andfins 20 are disposed alternatively to form a provisionally assembledcore portion 3. Then, this provisionally assembled core portion 3 isbrazed in a state in which a Zn inclusion, such as an Al—Zn alloy plate,a Zn plate, or Zn powder, is disposed near the other side of the coreportion 3, i.e., the rear side of the core portion when mounted to avehicle. In the illustrated example, an Al—Zn alloy plate 30 is used. Inthis method, Zn evaporates from the Zn inclusion by heating, and theevaporated Zn adheres to the heated fin 20. Then, the Zn will diffuse inthe fin 20. The amount of Zn to be given to the fin 20 is influenced bythe surface area of the Zn inclusion, the Zn concentration of the Zninclusion, the distance between the Zn inclusion and the core portion 3.Therefore, the Zn concentration of the fin 20 becomes high at the otherside portion 20 b near the Zn inclusion and gradually decreases towardthe one side portion 20 a. In cases where you do not wish to fuse the Zninclusion at the time of brazing, it is preferable to use an Al—Zn alloyplate, especially an Al—Zn alloy plate containing Zn: 5 to 50 mass %.The amount of Zn to be given to the fin 20 can be adjusted by the Zncontent in the Al—Zn alloy plate 30 and the distance from the coreportion 3.

In the case of using a Zn sprayed tube 10, the Zn evaporated from thesprayed layer will be supplied to the fin. However, since the sprayedlayer is evenly given to the tube 10 in the widthwise direction, the Znwill be evenly supplied to the fin in the widthwise direction thereof.Accordingly, it is considered that the Zn would barely exert aninfluence on forming pitting potential difference between the one sideportion 20 a and the other side portion 20 b, though the Zn may exert aninfluence on pitting potential.

Furthermore, the Zn contained in the fin 20 before brazing willevaporate to be decreased by heating at the brazing operation.Accordingly, controlling the evaporation amount of Zn at the other sideportion 20 b of the fin 20 can make Zn concentration difference in thefin 20. In concrete, flux is applied only to the other side portion 20 bof the fin 20 constituting the provisionally assembled core portion 3and then the provisionally assembled core portion 3 is heated to bebrazed. As a result that the Zn evaporation from the fin 20 isrestrained at the other side portion 20 b, the Zn concentration becomesrelatively low at the one side portion 20 a and relatively high at theother side portion 20 b.

Examples of the aforementioned flux include KF—AlF₃ composite, KAlF₄,K₂AlF₅, K₃AlF₆, AlF₃, CsF, BiF₃, LiF, KZnF₃, ZnF₂, and ZnCl₂. Amongother things, in the case of using flux containing Zn, since the Zncontained in the flux will diffuse into the fin, in addition to theaforementioned evaporation restraining effect, an effect of enhancingthe Zn concentration in the fin can be attained. The flux applyingmethod is not specifically limited, and can be performed by anywell-known method such as an immersion coating and a spraying method.

The aforementioned Zn adding or Zn evaporation restraining by partiallyapplying flux at the time of brazing can be performed independently orin combination with disposing the Al—Zn alloy plate 30 near the coreportion 3 to which flux is partially applied. Although the aboveexplanation is directed to the case in which a single fin 20 is disposedbetween adjacent tubes 10 and 10, the aforementioned processing can alsobe applied to the case in which two separated fins different in Znconcentration are used to form the one side fin 21 a with lower Znconcentration and the other side fin 21 b with higher Zn concentration.Furthermore, the Zn adding and/or the Zn evaporation restraining can beexecuted against two fins different in Zn concentration, which increasesthe Zn concentration difference therebetween.

In the heat exchanger manufacturing method according to the presentinvention, since Zn can be given to the fin by using the Al—Zn alloyplate or the Zn contained flux, pitting potential difference can beattained even in the case in which no Zn is contained in the finmaterial before brazing. However, in order to attain a prescribed Znconcentration difference and therefore to create a predetermined pittingpotential difference, it is preferable that a fin is manufactured usingZn contained aluminum alloy and then Zn concentration of the fin isadjusted by the aforementioned method at the time of brazing.

In the heat exchanger and the manufacturing method according to thepresent invention, it is preferable to use JIS 1xxx series aluminumalloy, aluminum alloy containing small amount of Cu and Mn, and JIS 3xxxseries aluminum alloy, as the material of the tube. Furthermore, a tubein which a brazing layer is formed on a core material made of theaforementioned aluminum alloy, or a Zn sprayed tube as a corrosionresistance tube can also be used arbitrarily. As for the fin, a bare finwith no brazing material clad or a brazing fin with brazing materialclad can be used.

EXAMPLES

Next, concrete examples of heat exchangers according to the presentinvention will be explained.

As a tube material, using aluminum alloy consisting of Cu: 0.4 mass %,Mn: 0.2 mass % and the balance being Al and inevitable impurities, flatmulti-bored tubes as shown in FIGS. 2 and 3 were extruded, and then Znwas thermally sprayed on both flat portions of each tube immediatelyafter the extrusion to thereby obtain Zn sprayed tubes 10. In thefollowing Examples and Comparative Examples, these Zn sprayed tubes 10were commonly used. As a fin, a brazing fin with a total thickness of100 μm in which a 10 μm thick Al—Si series alloy brazing material wasclad on both surfaces of an 80 μm thick core material made of variouscompositions containing Zn and Mn was used.

Example 1, Comparative Examples 2 & 3

As shown in FIG. 3, two fins different in fin core composition, one sidefin 21 a and the other side fin 21 b, were disposed between the adjacenttubes 10 and 10 along the longitudinal direction of the tube 10 with afin distance D of 1.5 mm to obtain a provisionally assembled coreportion 3.

KAl₄ as flux was applied to the entire provisionally assembled coreportion 3 by spraying, and then the core portion 3 was subjected toheating of 600° C.×10 min in a brazing furnace to braze the tube 10 andfins 21 a and 21 b.

In Table 1 shown below, the fin core compositions of the one side fin 21a and the other side fin 21 b and the Zn concentration difference inthese compositions after the brazing are shown.

Examples 2, 5, 6 & 8

As shown in FIG. 2, a single fin 20 was disposed between the adjacenttubes 10 and 10 to thereby obtain a provisionally assembled core portion3.

KAl₄ as flux was applied to the entire provisionally assembled coreportion 3 by spraying, and then the core portion 3 was subjected toheating of 600° C.×10 min in a brazing furnace in a state in which anAl-20% Zn alloy plate 30 was disposed 10 mm apart from the one side ofthe core portion 3. In this heating for brazing, the Zn evaporated fromthe Al—Zn alloy plate 30 adhered to the fin 20 and then diffused intothe fin 20. Since the Zn diffusion amount becomes smaller as thedistance from the Al—Zn alloy plate 30 increases, the Zn concentrationalong the widthwise direction of the Zn diffusion amount becamerelatively lower at the one side portion 20 a of the fin 20 apart fromthe Al—Zn alloy plate 30 and higher at the other side portion 20 b ofthe fin 20 near the Al—Zn alloy plate 30.

In Table 1 shown below, the fin core compositions of the one sideportion 20 a of the fin 20 and the other side portion 20 b of the fin 20and the Zn concentration difference in these compositions after thebrazing are shown.

Examples 3 & 4

As shown in FIG. 3, two separate fins 21 a and 21 b were disposedbetween the adjacent tubes 10 and 10 with a fin distance D of 1.5 mm toobtain a provisionally assembled core portion 3. Then, KAl₄ as flux wasapplied to the entire provisionally assembled core portion 3 byspraying.

Then, the core portion 3 was subjected to heating of 600° C.×10 min in abrazing furnace in a state in which the Al—Zn alloy plate 30 (shown inFIG. 2) was disposed near the one side fin 21 b of the core portion 3 tobraze the tube 10 and fins 21 a and 21 b.

In brazing the core portion 3, the core material composition of two finsbefore brazing, the Zn content of Al—Zn alloy plate 30 and the distancefrom the Al—Zn alloy plate to the core portion were adjusted. As aresult, the fin core material compositions of the one side fin 21 a andthe other side fin 21 b, the Zn concentration difference in thecompositions after the brazing are shown in Table 1.

Example 7

As shown in FIG. 3, two fins 21 a and 21 b were disposed between theadjacent tubes 10 and 10 with a fin distance D of 1.5 mm to obtain aprovisionally assembled core portion 3.

Then, KZnF₃ as flux was applied only to the other side fin 21 b of theprovisionally assembled core portion 3 by spraying, and then theprovisionally assembled core portion 3 was subjected to heating of 600°C.×10 min in a brazing furnace to braze the tube 10 and fins 21 a and 21b.

During the brazing of the core portion 3, since the Zn evaporation inthe other side fin 21 b was restrained by the flux applied on the otherside fin 21 b, the fin core material composition at the one side fin 21a and the other side fin 21 b and the Zn concentration difference in thecomposition after the brazing became as shown in Table 1.

Comparative Example 1

As shown in FIG. 2, a single fin 20 was disposed between the adjacenttubes 10 and 10 to obtain a provisionally assembled core portion 3.

Then, KAl₄ as flux was applied to the entire provisionally assembledcore portion 3 by spraying, and then the provisionally assembled coreportion 3 was subjected to heating of 600° C.×10 min in a brazingfurnace to braze the tube 10 and fins 21 a and 21 b.

By the heating for brazing, the fin core material composition at the oneside portion 20 a of the fin 20 and the other side portion 20 b of thefin 20 after the brazing became as shown in Table 1.

[Method of Measuring Pitting Potential Difference]

As to each heat exchanger manufactured as mentioned above, the pittingpotential difference between the one side portion 20 a and the otherside portion 20 b of the fin 20 was measured. In Examples 1, 3, 4 and 7and Comparative Example 1, the pitting potential was measured in thestate in which only the non-louvered portions located at both ends shownby the reference numerals 22 a and 22 b in FIG. 2 were exposed, and thedifference thereof was obtained. The pitting potential measurement wasperformed in a water solution of 2.67% AlCl₃ at the potential sweep rateof 20 mV/min.

[Corrosion Test]

To each heat exchanger manufactured as mentioned above, SWAAT testdefined in ASTM-G85-A3 was performed. In the test, using corrosion testliquid adjusted to pH 3 by adding acetic acid to artificial sea water byASTM D1141, a cycle of spraying the corrosion test liquid for 0.5 hourand leaving the wet state for 1.5 hours was repeated for 200 hours.

[Method of Measuring Fin Strength]

After the corrosion test, the heat exchanger was cut into halves at thewidthwise central portion of the tube to obtain one side portion 20 a ofthe fin 20 with higher pitting potential and the other side portion 20 bof the fin 20 with lower pitting potential. The tensile strength of eachof the one side portion 20 a and the other side portion 20 b wasmeasured. The measuring of the tensile strength was performed whileholding the tube 10. The measured tensile strength in ComparativeExample 1 was used as a standard, and the results are shown as follows:

“×”: the tensile strength was less than 1.0 times of the tensilestrength in Comparative Example;

“◯”: the tensile strength was larger than 1.0 times of the tensilestrength in Comparative Example but less than 1.5 times thereof; and

“⊚”: the tensile strength was more than 1.5 times of the tensilestrength in Comparative Example. TABLE 1 Composition of Composition ofthe other side Tensile one side portion portion(the Pitting strength of(one side fin) other side fin) Zn concentration Zn concentrationpotential one side (mass %)* (mass %)* difference difference differenceportion Fin Zn Mn Zn Mn forming method (mass %) (mV) (fin) Example 1 2pieces 1.2 1.5 2 1.5 Fin composition 0.8 120 ⊚ before brazing 2 1 piece1.2 1.5 1.7 1.5 Al—Zn plate 0.5 40 ⊚ 3 2 pieces 1 1.5 2.5 1.5 Al—Znplate 1.5 180 ⊚ 4 2 pieces 1 1.3 2 1.3 Al—Zn plate 1 150 ⊚ 5 1 piece 11.8 1.5 1 Al—Zn plate 0.5 50 ⊚ 6 1 piece 1.8 1.5 2.5 1.5 Al—Zn plate 0.780 ⊚ 7 2 pieces 2 1.5 2.5 1.5 Flux partially 0.5 40 ⊚ sprayed 8 1 piece2.1 1.5 2.6 1.5 Al—Zn plate 0.4 40 ◯ Comp. Ex. 1 1 piece 2.5 1.5 2.5 1.5— 0 0 X 2 2 pieces 2.4 1.5 2.5 1.5 Fin composition 1.5 20 X beforebrazing 3 2 pieces 1 1.5 3.5 1.5 Fin composition 1.5 300 X beforebrazing*the balance being Al and inevitable impurities

From the results shown in Table 1, it is confirmed that the fin strengthat the one side portion with higher pitting potential can be restrainedeven after an occurrence of corrosion and therefore certain strength canbe maintained by forming a pitting potential difference between the oneside portion of the fin and the other side portion of the fin along thewidthwise direction.

Accordingly, in cases where the heat exchanger according to eachembodiment is used for an automobile air-conditioner, by installing theheat exchanger to a vehicle such that the one side portion of the finwith higher strength faces toward the front side of the vehicle, itbecomes possible to prevent or delete fin damages due to chippings.

INDUSTRIAL APPLICABILITY

The heat exchange can maintain the strength at the one side portion ofthe fin even if corrosion occurs to same extent since cathodicprotection is given to the one side portion of the fin. Therefore, theheat exchanger can be preferably utilized as a heat exchanger for use ina vehicle such as an automobile.

BROAD SCOPE OF THE PRESENT INVENTION

While the present invention may be embodied in many different forms, anumber of illustrative embodiments are described herein with theunderstanding that the present disclosure is to be considered asproviding examples of the principles of the invention and such examplesare not intended to limit the invention to preferred embodimentsdescribed herein and/or illustrated herein.

While illustrative embodiments of the invention have been describedherein, the present invention is not limited to the various preferredembodiments described herein, but includes any and all embodimentshaving equivalent elements, modifications, omissions, combinations(e.g., of aspects across various embodiments), adaptations and/oralterations as would be appreciated by those in the art based on thepresent disclosure. The limitations in the claims are to be interpretedbroadly based on the language employed in the claims and not limited toexamples described in the present specification or during theprosecution of the application, which examples are to be construed asnon-exclusive. For example, in the present disclosure, the term“preferably” is non-exclusive and means “preferably, but not limitedto.” In this disclosure and during the prosecution of this application,means-plus-function or step-plus-function limitations will only beemployed where for a specific claim limitation all of the followingconditions are present in that limitation: a) “means for” or “step for”is expressly recited; b) a corresponding function is expressly recited;and c) structure, material or acts that support that structure are notrecited. In this disclosure and during the prosecution of thisapplication, the terminology “present invention” or “invention” may beused as a reference to one or more aspect within the present disclosure.The language present invention or invention should not be improperlyinterpreted as an identification of criticality, should not beimproperly interpreted as applying across all aspects or embodiments(i.e., it should be understood that the present invention has a numberof aspects and embodiments), and should not be improperly interpreted aslimiting the scope of the application or claims. In this disclosure andduring the prosecution of this application, the terminology “embodiment”can be used to describe any aspect, feature, process or step, anycombination thereof, and/or any portion thereof, etc. In some examples,various embodiments may include overlapping features. In this disclosureand during the prosecution of this case, the following abbreviatedterminology may be employed: “e.g.” which means “for example;” and “NB”which means “note well.”

1. A heat exchanger having a core portion in which aluminum flat tubesand aluminum fins are disposed alternatively and brazed with each other,each fin having a one side portion located at one side of the tube andthe other side portion located at the other side of the tube, whereinthe one side portion of the fin is higher in pitting potential than theother side portion of the fin, and wherein the pitting potentialdifference between the one side portion of the fin and the other sideportion of the fin is 40 to 200 mV.
 2. The heat exchanger as recited inclaim 1, wherein the pitting potential difference is created by Znconcentration difference in aluminum alloy constituting the fin.
 3. Theheat exchanger as recited in claim 2, wherein the Zn concentrationdifference is 0.4 mass % or more.
 4. The heat exchanger as recited inclaim 1, wherein the one side portion of the fin and the other sideportion of the fin are constituted by separated fins consisting of oneside fin located at one side of the tube and the other side fin locatedat the other side of the tube, the separated fins being disposed with adistance therebetween along the longitudinal direction of the tube. 5.The heat exchanger as recited in claim 4, wherein the distance betweenthe one side fin and the other side fin is 3 mm or less.
 6. The heatexchanger as recited in claim 4, wherein the one side fin is made ofaluminum alloy consisting essentially of Mn: 0.8 to 2 mass %, Zn: 0.4 to2 mass %, and the balance being Al and inevitable impurities, andwherein the other side fin is made of aluminum alloy consistingessentially of Mn: 0.8 to 2 mass %, Zn: 1.5 to 3 mass %, and the balancebeing Al and inevitable impurities.
 7. The heat exchanger as recited inclaim 1, wherein the one side portion of the fin and the other sideportion of the fin are made of an integrated single fin, wherein pittingpotential difference is formed between the one side portion and theother side portion.
 8. The heat exchanger as recited in claim 7, whereinthe one side portion of the fin is made of aluminum alloy consistingessentially of Mn: 0.8 to 2 mass %, Zn: 0.4 to 2 mass %, and the balancebeing Al and inevitable impurities, and wherein the other side portionof the fin is made of aluminum alloy consisting essentially of Mn: 0.8to 2 mass %, Zn: 1.5 to 3 mass %, and the balance being Al andinevitable impurities.
 9. The heat exchanger as recited in claim 1,wherein the fin has a thickness of 100 μm or less.
 10. A heat exchangerfor use in a vehicle, the heat exchanger having a core portion in whichaluminum tubes and aluminum fins are disposed alternatively and brazedwith each other, each fin having one side portion located at one side ofthe tube and the other side portion located at the other side of thetube, wherein the one side portion of the fin is higher in pittingpotential than the other side portion of the fin, wherein the pittingpotential difference between the one side portion of the fin and theother side portion of the fin is 40 to 200 mV, and wherein the heatexchanger is installed on a vehicle with the one side portion of the finwith higher pitting potential facing toward a front side of the vehicleand the other side portion of the fin with lower pitting potentialfacing toward a rear side of the vehicle.
 11. A method of manufacturinga heat exchanger having a core portion in which aluminum flat tubes andaluminum fins are disposed alternatively and brazed with each other,each fin having one side portion located at one side of the tube and theother side portion located at the other side of the tube, the one sideportion of the fin being higher in pitting potential than the other sideportion of the fin, the method, comprising the steps of: provisionallyassembling a core portion by alternatively disposing the tubes and thefins; and heating the provisionally assembled core portion in a furnaceto braze the tubes and the fins.
 12. A method of manufacturing a heatexchanger having a core portion in which aluminum flat tubes andaluminum fins are disposed alternatively and brazed with each other,each fin having one side portion located at one side of the tube and theother side portion located at the other side of the tube, the one sideportion of the fin being higher in pitting potential than the other sideportion of the fin, the method, comprising the steps of: provisionallyassembling a core portion by alternatively disposing the tubes and thefins; and heating the provisionally assembled core portion in a furnacein a state in which an Al—Zn alloy plate is disposed neat the other sideportion of the fin to braze the tubes and the fins.
 13. A method ofmanufacturing a heat exchanger having a core portion in which aluminumflat tubes and aluminum fins are disposed alternatively and brazed witheach other, each fin having one side portion located at one side of thetube and the other side portion located at the other side of the tube,the one side portion of the fin being higher in pitting potential thanthe other side portion of the fin, the method, comprising the steps of:provisionally assembling a core portion by alternatively disposing thetubes and the fins; applying flux only to the other side portion of thefin of the provisionally assembled core portion; and heating theprovisionally assembled core portion to which the flux is applied to theother side portion of the fin in a furnace to braze the tubes and thefins.
 14. The heat exchanger as recited in claim 5, wherein the one sidefin is made of aluminum alloy consisting essentially of Mn: 0.8 to 2mass %, Zn: 0.4 to 2 mass %, and the balance being Al and inevitableimpurities, and wherein the other side fin is made of aluminum alloyconsisting essentially of Mn: 0.8 to 2 mass %, Zn: 1.5 to 3 mass %, andthe balance being Al and inevitable impurities.